Software Engineering For Students: A Programming Approach Part 44 pps

408 Appendix A ■ Case studies The user must first offer up their card to the reader. The display then asks the user to enter their PIN, via the keyboard. If this is successful, the display presents a set of options. The system must be highly robust, since it is to be used by untrained bank customers in public places. This is an example of general-purpose software that would be used by a large number of diverse people. The word processor provides facilities for its user to enter text, amend text, save text, print text and retrieve a saved document from a file. The word processor displays a blank panel which displays text entered from the keyboard. The user can: ■ save the document in a specified file ■ retrieve a document from a specified file ■ print the document. A document consists of sentences ending in a period character. A paragraph consists of zero or several sentences ending in a special end-of-paragraph character. A new page break can be inserted anywhere within a document. A section of text can be selected by clicking just before the start of some text, then dragging the cursor with the button down. Selected text is shown highlighted. The clip board is a temporary storage that is not visible. Commands are provided to: ■ cut selected text and copy it to the clip board, replacing any text already in the clip board ■ copy selected text to the clip board, replacing any text already in the clip board ■ paste text at the cursor position from the clip board. A document can be displayed either as raw text or as formatted text suitable for printing. Cyberspace invaders is a variation of a game that was popular in the early days of com- puter games. This software is appealing because it has a fun user interface. It is also easy to see a connection between the visual appearance and the software structure. The spec- ification is as follows. A window displays a defender and an alien (Figure A.1). The alien moves sideways. When it hits a wall, it reverses its direction. The alien randomly launches a bomb that moves vertically downwards. If a bomb hits the defender, the user loses and the game A.3 ● Computer game A.2 ● The word processor BELL_Z02.QXD 1/30/05 4:32 PM Page 408 A.4 The library 409 is over. The defender moves left or right according to mouse movements. When the mouse is clicked, the defender launches a laser that moves upwards. If a laser hits the alien, the user wins and the game is over. A button is provided to start a new game. This application is a typical information system. Software is required to maintain information about books held in a library. The sys- tem is intended for use by the library staff. The software must run on standard networked PCs. There may be up to 20 PCs on the library network. For each book, the following information is held in the computer: ■ title ■ author ■ ISBN A.4 ● The library Figure A.1 Cyberspace invaders BELL_Z02.QXD 1/30/05 4:32 PM Page 409 410 Appendix A ■ Case studies ■ year ■ borrower identification (if on loan) ■ date of issue (if on loan). The computer should be able to store information on up to 100,000 books. The computer system should provide facilities to: ■ issue a book to a borrower ■ receive a book returned by a borrower ■ create information about a newly acquired book ■ display a list of the books on loan to a particular borrower. The facilities should be accessible via a GUI. The computer must respond within one second to any request. The system should provide a search facility to find out whether the library possesses a particular book. With suitable security precautions, the system will initialize the library information so that it contains zero books. When a book becomes overdue, the system should display appropriate information. The system should provide secure access by only the library staff. The software must be delivered by such-and-such a date and cost no more than $100,000. It must be fully documented and easy to maintain. This is an example of a safety-critical system. Other similar systems include a control sys- tem for a power station and a fly-by-wire system for an airplane. A computer system monitors the vital signs of a patient in a hospital. Sensors attached to a patient continually send information to the computer: ■ heart rate ■ temperature ■ blood pressure. Some of the readings require conversion to useful units of measurement (e.g. micro volts into degrees centigrade). The computer displays the information on a screen. It also logs the information in a file that can be retrieved and displayed. If any of the vital signs exceed safe limits, the screen flashes a warning and an alarm sounds. The limits have default values, but can also be changed by the operator. If a sensor fails, the screen flashes a warning and the alarm sounds. A.5 ● Patient monitoring system BELL_Z02.QXD 1/30/05 4:32 PM Page 410 Within the field of software engineering, different people use terms differently. The fol- lowing are the meanings of terms as used in this book. development approach – a particular collection of tools, methods and work styles that are used in carrying out software development development life cycle – the complete process of software development from inception through to release and maintenance of the product development process – specific activities that are carried out during software development maintenance – fixing bugs, responding to changed requirements and upgrading the software for a new platform method – the term for a procedure, subprogram or subroutine methodology 1. the study of methods, or 2. a collection of methods, techniques and notations used for software development portability 1. the degree to which a piece of software runs on different platforms (machine and/or operating system), or 2. the issue of whether software needs to run on different platforms porting – moving a piece of software to a new platform process model – idealized plan of software development in general, or an analysis of the approach adopted for a particular software development project APPENDIX B Glossary BELL_Z03.QXD 1/30/05 4:33 PM Page 411 The Unified Modeling Language (UML) is a graphical notation for describing object- oriented software. It is not a method for design, but a notation that can help with designing software or help to document software once it is complete. This appendix gives a summary of those aspects of UML used in this book. UML is a large and potentially complex notation and therefore we have only used a part of the notation. Thus the diagrams described and used in this book are: ■ use case diagrams ■ class diagrams ■ package diagrams ■ activity diagrams. These diagrams describe, in outline, the use cases associated with a system. Figure C.1 shows an example of a use case diagram for users of a bank ATM. In this example there is a single type of user, a bank customer. A customer can ask the system to carry out either of two functions – withdraw cash and check balance. C.1 ● Use case diagrams APPENDIX C UML summary withdraw cash check balance Bank Customer Figure C.1 A use case diagram BELL_Z04.QXD 1/30/05 4:33 PM Page 412 C.2 Class diagrams 413 These describe classes and their interrelationships. Classes are shown as rectangles con- taining the class name. The simplest relationship is where a class uses another. For example, in Figure C.2, class Game uses classes Defender, Alien, Laser and Bomb. This means that Game creates objects from these classes and/or calls methods in objects created from these classes. A class diagram can also show the inheritance relationships between classes – the sub- classes and superclasses. As illustrated in Figure C.3, to show that a class extends another, a line is drawn from the subclass to the superclass, with the arrowhead pointing to the superclass. Thus Sprite is the superclass of both Alien and Bomb. If a class is an abstract class, the name of the class is written in italics. This can be dif- ficult to see, particularly when hand-written. So the name of an abstract class can be fol- lowed by the text {abstract} to clarify the meaning. An interface is described in the same way as a class – as a box. The difference is that the text <<interface>> precedes the name. A class that implements an interface has a dashed line with an arrow leading to the interface box (see Figure C.4). A class can be described in more detail, as illustrated in Figure C.5. There are three compartments in this type of class diagram. The first compartment holds the class C.2 ● Class diagrams Defender Alien Laser Bomb Game Figure C.2 Class diagram Sprite Alien Bomb Figure C.3 Class diagram showing inheritance BELL_Z04.QXD 1/30/05 4:33 PM Page 413 414 Appendix C ■ UML summary name, the second describes variables and the third describes methods. Any class (static) variables or methods are shown underlined. The visibility of an element can, optionally, be described in a prefix as in Java – public, private, protected or default. In keeping with information hiding, the diagram is often drawn with the second compartment (the variables) omitted. A package can be diagrammed as shown in Figure C.6. It is a rectangle with a tab at the top that holds the package name. Optionally, the classes within a package can be shown within the rectangle. This shows a class util that consists of classes Random, ArrayList and Stack. An activity diagram describes a sequence of activities. Thus an activity diagram can be used to show the flow of control through software. An activity diagram can show: ■ conditions (corresponding to if statements) ■ loops (corresponding to for and while statements) ■ concurrent activity (corresponding to threads). C.4 ● Activity diagrams C.3 ● Package diagrams <<interface>> StackInterface Stack Figure C.4 A class and its interface. The arrow should be hollow panel timer Game mouseMoved mouseClicked actionPerformed Figure C.5 Class diagram showing the detail of a class BELL_Z04.QXD 1/30/05 4:33 PM Page 414 C.4 Activity diagrams 415 An activity diagram can also be used to show a human activity, such as carrying out throwaway prototyping, Figure C.7. Actions are written in boxes with curved corners. The sequence of actions is shown by the arrows. A sequence starts with a special “blob” symbol. A sequence ends with a different symbol, as shown. util Stack Random ArrayList Figure C.6 A package diagram Construct prototype Check with user Refine prototype Deliver the specification Draw up an outline specification [User requires change] [User happy] Figure C.7 Activity diagram showing throwaway prototyping BELL_Z04.QXD 1/30/05 4:33 PM Page 415 416 Appendix C ■ UML summary This diagram also uses the diamond-shaped branch symbol. Associated with each output from the branch is a condition (termed a guard). If the condition is true, the route is taken – just as in an if statement. Further reading • Two very clear and readable books on UML are: Martin Fowler, UML Distilled, Addison-Wesley. Perdita Stevens, and Rob Pooley, Using UML, Addison-Wesley. BELL_Z04.QXD 1/30/05 4:33 PM Page 416 References to books and websites are given at the end of each chapter. This bibliogra- phy presents some general sources. Dates are not given because new editions of them are produced frequently. Here are the major books on the subject: Ian Sommerville, Software Engineering, Addison-Wesley. Carlo Ghezzi, Mehdi Jazayeri and Dino Mandrioli, Fundamentals of Software Engineering, Prentice Hall. Hans van Vliet, Software Engineering: Principles and Practice, John Wiley. Roger S. Pressman, Software Engineering, a Practitioner’s Approach, McGraw-Hill. The Software Engineering Institute at Carnegie Mellon University, USA, is a prestigious organization. They publish articles on software engineering topics and were the instigators of the capability maturity model. Their website is at: http://www.sei.cmu.edu/ Here are two short and simple books on UML: Martin Fowler, UML Distilled, Addison-Wesley. Perdita Stevens and Rob Pooley, Using UML, Addison-Wesley. UML Software engineering Bibliography BELL_Z05.QXD 1/30/05 4:34 PM Page 417 . flashes a warning and an alarm sounds. The limits have default values, but can also be changed by the operator. If a sensor fails, the screen flashes a warning and the alarm sounds. A. 5 ● Patient. (the variables) omitted. A package can be diagrammed as shown in Figure C.6. It is a rectangle with a tab at the top that holds the package name. Optionally, the classes within a package can be shown. game that was popular in the early days of com- puter games. This software is appealing because it has a fun user interface. It is also easy to see a connection between the visual appearance and